ὅτι ἤδη πάντα τετέλεσται. Cf. v. 30; Acts 13:29, ὡς δὲ ἐτέλεσαν πάντα τὰ περὶ αὐτοῦ γεγραμμένα; also Luke 22:37. Jesus had completed all the work he had been sent into the world to do; the revelation and the deed of love were complete. There is perhaps a special reference to the complete fulfilment of Scripture, with the note that one prophecy remains to be enacted.
The use of the singular, ἵνα τελειωθῇ ἡ γραφή, makes it probable that this final clause is to be connected with what follows. It is not impossible, but less likely, that it should be connected with what precedes: All things had been accomplished in order that the Scripture should be fulfilled. The unusual τελειοῦν is used instead of πληροῦν, probably in view of the repeated τετέλεσται.
διψῶ. See Ps. 69 (68):22, εἰς τὴν δίψαν μου ἐπότισάν με ὄξος (quoted in 1QH 4.11). There can be little doubt that this is the γραφή in mind. In no other gospel does Jesus declare his own thirst—in John as usual he takes the initiative. In Mark a sponge of vinegar is offered (Mark 15:36, γωμίσας σπόγγον ὄξους περιθεὶς καλάμῳ ἐπότιζεν αὐτόν; cf. Matt. 27:48; Luke 23:36) As in the mention of the casting of lots for the clothes of Jesus John makes the Old Testament allusion more explicit than do the earlier evangelists. He is probably dependent on Mark or a similar source, and whether the Marcan incident is historical narrative or a construction based simply on the Old Testament passage is a question that need not be discussed here.
. . .
30. τετέλεσται. See on this word in v.
28, and cf. the use of τελειοῦν in Hebrews. Now that the last prophecy had been
fulfilled it could be spoken by Jesus himself. His work was done. The cry is to
be thought of in this positive sense, not as the mere announcement of the
imminence of death, though this too is intended—the word bears a
characteristically Johannine double meaning. If it once was the concluding
formula of a mystery it has been very thoroughly historicized and
Christianized. Cf. 4:34; 17:4, ἐγώ σε ἐδόξασα ἐπὶ τῆς γῆς, τὸ ἔργον τελειώσας ὃ
δέδωκάς μοι ἵνα ποιήσω; also 13:1 (εἰς τέλος). (C.K. Barrett, Gospel
According to St. John: An Introduction with Commentary and Notes on the Greek
Text [2d ed.; London: SPCK, 1978], 553, 554)
Further Reading:
Full Refutation of the Protestant Interpretation of John 19:30